Conventionally, it is known that, in such an electromagnetic fuel injection valve in which the movable core is attached directly onto the fixed core upon energization of the coil and a valve-opening limit for the valve body is thereby defined, since a large impact is imposed on the attached surfaces when the cores are attached to each other, a Cr, Mo, or Ni plating layer is formed in order to ensure abrasion resistance, as is disclosed in, for example, Patent Document 1. Furthermore, in order to avoid the two cores making contact with each other when the coil is energized, providing a stopper plate on the valve housing in order to define a valve-opening limit for the valve body is also known as disclosed in Patent Document 2.
[Patent Document 1] Japanese Patent Application Laid-open No. 63-125875
[Patent Document 2] Japanese Patent Application Laid-open No. 2002-89400
Such plating layers on the movable and fixed cores as disclosed in Patent Document 1 have to be formed by a plating step, which requires a long processing time; moreover, since the thickness of the plating layers is variable, it is necessary to correct the dimensions by polishing the plating layers, the number of steps increases, and it is difficult to reduce the cost of the electromagnetic fuel injection valve. Furthermore, as disclosed in Patent Document 2, providing the stopper plate on the valve housing results in increases in the number of components and the number of assembly steps, and this is also disadvantageous in terms of reducing the cost.
Patent Documents 3 to 5 below also disclose art related to electromagnetic fuel injection valves.
[3] Japanese Patent Application Laid-open No. 2002-4013
[4] Japanese Patent Application Laid-open No. 59-221456
[5] Japanese Patent Application Laid-open No. 9-303230
Patent Document 3 teaches a valve member having a movable core provided at one end thereof, the movable core abutting directly against an attracting face of a fixed core, and a valve portion provided on the other end of the valve member is housed in a valve seat member housed in a valve housing. There is no arrangement for alleviating the impact when the two cores are attracted to each other and, furthermore, a lengthwise hole is formed only in an upper part of the interior of the valve member, and there is no arrangement shown for reducing the weight and thus improving the responsiveness by means of this design.
Patent Document 4 shows a structure in which parts of a fixed core and a movable core that are attracted to each other are each press-fitted to a ring formed from a ceramic, etc., and when a valve is opened the ring projecting from the movable core is made to abut against the ring fixed to the fixed core. It is necessary to individually carry out mounting and fixing of the ring to the fixed core and the ring to the movable core, and forming such rings from a ceramic, etc. makes the structure complex and the assembly difficult and complicated. There are many factors that influence valve characteristics, such as adjustment of the amount of the ring projecting from the movable core and adjustment of the gap between the two rings, and the influence on the flow rate is a problem. Since the valve body does not have a journal portion for restricting movement thereof, the centering is poor, and the valve closing characteristics are variable.
Patent Document 5 teaches an arrangement in which a lengthwise hole is provided within a cylindrical valve body, and a lateral hole communicating with the lengthwise hole is formed in the vicinity of a valve portion of the valve body. Since the valve portion is conical, the centering is poor, and the valve closing characteristics are variable.